1. Field of the Invention
The invention relates to a process for the preparation of cellular polymers having urethane groups, isocyanurate groups, or both. The polymers are prepared by reacting organic polyisocyanates with compounds having reactive hydrogen atoms which are used in the form of storage-stable crystalline suspensions.
2. Description of the Prior Art
It is known that polyurethane foams with various physical properties can be prepared by reacting compounds having at least two active hydrogen atoms, particularly polyols, with polyisocyanates. Reinforcing agents, chain extenders, cross-linking agents, blowing agents, activators, emulsifiers and other additives may also be incorporated into the reaction mixture. With suitable selection of the components, flexible as well as rigid foams can be prepared. However, it is known in the art that polyurethane foams are not thermally stable at high temperatures.
It is also known that urethane group-containing polyisocyanurates can be prepared by the reaction of polyisocyanates to form ring structures. The reaction may be carried out in the presence of auxiliaries and catalysts. The resultant isocyanurates are reacted with polyols to prepare rigid foams. It is often advantageous to carry out the polyaddition reaction of polyols contemporaneously with the polyisocyanurate reaction.
Rigid foams having urethane and isocyanurate groups are very useful because of their good thermal stability, as well as their optimum insulating capacity. They are well suited for use as insulating materials for the refrigeration industry, construction industry, and others. This is because isocyanurate bonds are thermally more stable than urethane bonds and result in polymers with increased ignition temperature. However, the problem with using these materials is that the polyisocyanurate rigid foams are more brittle and have a lower abrasion resistance.
Because of the problems associated with polyurethane and polyisocyanurate rigid foams which are known in the art, there is a need to develop rigid foams which have increased heat resistance, are less brittle, and have an improved resistance to abrasion. These requirements must be achieved without sacrificing compression strength in and perpendicular to the foaming direction.